Lets be honest it was complete nonsense. There was probably a conversation that went something like
Weiss: Right gang, it's episode 9, we need something to get people to #OMG on twitter
Benioff: How about Rape?
Weiss: I like your thinking... but we went to that well already this season, we might need to change it up a bit
Benioff: ... Dragon Rape?
Weiss: ....... I'll get back to you...
Writer: I know! We can kill someone! People always think its awesome when we kill people... because they die, and nobody dies on tv... so its cool! people will love it.
Weiss: Hmmm... Well we already killed Sean Connery this year, so it needs to be a good one...
Writer: Child death! That'll put the shit up them! How about that kid on the wall... erm, Oni? Ori?
Weiss: Oh you mean Ozzy. No, people will actually like that... let's kill Stannis' kid...
Writer: .... But why would he want to kill someone he's expressively told us he loves unquestionably, that he would, and has in the past, done anything to keep alive? Not only that, but she's the last of his blood line, and the heir to the throne he's trying to win....
Weiss: Erm.... because he's desperate?
Writer: Why is he desperate? He has loads of men, he's the greatest commander in Westeros! I mean we already flirted with the idea that he's an idiot by making him march down in the snow in the first place...
Weiss: Well... super Ramsay's going to start a fire and shit. Yeah, that'll make him desperate
Writer: .... How the feck's he going to do that?
Weiss: Stop getting bogged down in specifics... he's desperate, they kill the kid, done.
Benioff: And then she gets raped. Top stuff.